Abstract: Endogenous release from the sediments in small lakes is a major cause of excessive nitrogen and phosphorus concentrations in the overlying water; however, research in this area remains insufficient. To investigate the mechanisms of release of nitrogen and phosphorus from sediments affecting water quality, we took Jiaolu Lake, a typical small lake severely polluted by nitrogen and phosphorus, as a case study. Sediment samples from the upper 90 cm were collected and simulated release experiments at different depths (0~90 cm) under varying environmental conditions (temperature, pH, and dissolved oxygen) were conducted to examine their effects on the release of total phosphorus (TP) and total nitrogen (TN) from the sediments. The results indicate that TP and TN in the 0~30 cm sediment layer are at severely polluted levels (TP: 996.47~1 083.69 mg/kg; TN: 2 097.24~2 169.89 mg/kg), and their release has the most significant impact on the overlying water. TP release decreases with increasing depth, while TN release remains largely unchanged with depth. Environmental conditions exert a significant regulatory effect on nitrogen and phosphorus release: both rising temperature and decreasing dissolved oxygen promote nitrogen and phosphorus release. TN release decreases with increasing pH, while TP release is weakest under neutral conditions. The study clarifies that endogenous release from sediments is a key factor contributing to persistent water pollution, and the findings provide a scientific basis for the management of small eutrophic lakes.